1. Field of the Invention
This invention relates to sewer grates commonly located near the curbs of paved roads for carrying away surface water. The invention is more particularly concerned with mechanisms for locking such grates in their mounting frames to prevent their theft.
2. Prior Art
Sewer grates are located along paved roadways to transport surface water into the underground storm drains. Such grates are commonly constructed out of cast iron. A typical grate has parallel spaced bars in a grid pattern, with the openings between the bars suited for receiving surface water. The upper surface of the grate is level with the road surface (i.e. the pavement).
Each grate is mounted on a cast iron frame embedded in the concrete pavement surface near the curb. The grate is commonly seated on an interior ledge in the frame, such that the grate can be readily removed, e.g. when it becomes necessary to clean out the storm drain.
A sewer grate usually weighs about one hundred fifty pounds. In spite of such a large weight, the grates are quite often stolen or at least removed from the mounting frames, as an act of vandalism. Thieves sell such grates to metal scrap dealers.
The stolen (removed) grates must be replaced, with consequent expense to the city. Also, before a replacement grate is installed, there is a potential danger that a vehicle (car or truck) will have its front or rear wheels pass over the drain opening. The impact damages the wheel and/or the vehicle suspension; personal injury damage can also occur. Motorists often sue the city government for negligence attributable to missing sewer grates. The opening created by a missing sewer grate is large enough that a small child can conceivably fall into the sewer, and be injured.
The following prior art represents attempts to anchor or lock a manhole cover in position to prevent theft.
5,065,955SpiessLocking Device forCoverings for Manholesand Other Ground Openings4,973,191DannhauserManhole Cover5,071,177SpiessLocking Device forthe Positive Holding of aCover or Grate in Frame4,964,755LewisManhole Cover Lock Apparatus5,082,392MarcheseManhole Cover Lock with SpringBiased Locking Bars4,763,449VigneronManhole Cover Sealing and LockingArrangement3,279,838HamiltonLocking Securement forSheet Metal HousingCover4,723,866McCauleyManhole Cover LockingBolt ConstructionIn practice, it is believed the structures disclosed these in patents are either expensive, complicated or ineffective.
U.S. Pat. No. 4,723,866 which was issued Feb. 9, 1988 to Durham McCauley shows a manhole cover locking mechanism with a special bolt head requiring a specially constructed wrench.
U.S. Pat. No. 3,279,838, which issued Oct. 18, 1966 to Douglas L. P. Hamilton, shows a locking bolt head having a diagonal opening with a central pin that requires an Allen wrench with a central cavity for receiving the pin when the Allen wrench is inserted in the opening.